I don’t see any harm in bringing back something that’s been gone since what, 2018? 7 years is long enough for anything’s exclusivity to no longer be a selling point.
Meanwhile, the mage tower appearances would be a major selling point right now for people who weren’t around during Legion or who weren’t ready or able to get them at the time.
Not bringing them back is a major marketing fail. But my guess is that Blizz devs must not be able to do the mage tower in Remix because why else would they decide not to release a popular feature?